Project Summary/Abstract Several studies have explored associations of air pollution with autism spectrum disorders (ASD), with all but one suggesting that some aspect of air pollution increases the risk of ASD, but details of this association remain uncertain. While these studies have found associations with, in particular, traffic-related pollutants and particulate matter (PM), they have in general been relatively small and most have been limited to California. One study in Taiwan, one in Sweden (among twins), and one combining several European cohorts are the only non-U.S. studies, and they came to different conclusions. More exploration of these exposures are needed outside the U.S. context. Furthermore, understanding critical windows of exposure, and susceptible populations is critical. A study of ours and one other have suggested effects specific to the 3rd trimester. Prior work of ours has also suggested that associations with air pollutants may be specific to boys, but the numbers of ASD cases among girls were too small to adequately address this. Our goal is to examine the basic question of the association between maternal exposure to air pollutants and ASD, and details of any association, in a very large cohort in a very different setting: the population of Israel. Israel represents a unique setting for the study of air pollutants and ASD for several reasons: 1) Air pollution levels are higher and with a wider range than in the US; 2) Dust storms occur sporadically that create very well timed extreme exposure events to a very different form of PM; 3) we have well-validated, highly resolved?in both space and time?models of both PM and nitrogen dioxide (NO2, a marker of traffic-related air pollution) exposure; and 4) the database is very large with over 8,000 ASD cases across the entire Israeli population going back several years. With these data we will examine the association between maternal exposure to PM, NO2, and dust storms and risk of ASD in her child. We will have exposure estimates on a weekly time scale and can examine susceptible windows of exposure in the perinatal period, and whether any association is specific to boys or modified by other key factors, such as whether the family is simplex or multiplex, to an extent not previously done.